Vinyl ferrocene butadiene copolymer burning rate catalyst

ABSTRACT

COPOLYMERS OF VINYL FERROCENE AND BUTADIENE ARE DISCLOSED ALONG WITH THE PROCEDURE FOR PREPARATION. THE COPOLYMERS ARE USEFUL AS A BURNING RATE CATALYST AND PROVIDE A MEANS FOR INTRODUCING AND MAINTAINING A HIGH CATALYST CONCENTRATION IN SOLID PROPELLANTS INASMUCH AS THE COPOLYMER CONTAINING THE IRON CATALYST IS CAPABLE OF SERVING AS THE BINDER REPLACING PART OF THE NORMALLY USED BINDERS IN SOLID PROPELLANTS. ALSO DISCLOSED IS A TYPICAL SOLID PROPELLANT COMPOSITION UTILIZING THE COPOLYMERS OF THIS INVENTION AS A BINDER REPLACEMENT AND BURNING RATE CATALYST.

United States Patent 3,770,787 VINYL FERROCENE BUTADIENE COPGLTMERBURNING RATE CATALYST Jimmy D. Burnett, Arab, Ala, assignor to theUnited States of America as represented by the Secretary of the Army NoDrawing. Original application Sept. 17, 1969, Ser. No. 858,896. Dividedand this application .luly 19, 1971, Ser. No. 164,143

lint. Cl. (307i 15/02 US. Cl. 260-439 CY 3 Claims ABSTRACT UP THEDISCLOSURE Copolymers of vinyl ferrocene and butadiene are disclosedalong with the procedure for preparation. The copolymers are useful as aburning rate catalyst and provide a means for introducing andmaintaining a high catalyst concentration in solid propellants inasmuchas the copolymer containing the iron catalyst is capable of serving asthe binder replacing part of the normally used binders in solidpropellants. Also disclosed is a typical solid propellant compositionutilizing the copolymers of this invention as a binder replacement andburning rate catalyst.

This application is a division of application Ser. No. 858,896, filedSept. 17, 1969.

BACKGROUND OF THE INVENTION The burning rates of solid propellantcompositions are increased when various metal containing compounds areused in the compositions. Iron oxides and iron-containing additives suchas vinyl ferrocene and n-butyl ferrocene have been used in solidpropellants to promote their burning rates. The liquid iron compoundshave been generally preferred to solid iron compounds because of theconvenience in mixing and blending. The liquid iron compounds haveprovided some additional benefit as plasticizing agents. 'In the liquidstate the ferrocenes have certain inherent disadvantages characteristicof any liquid additives; such disadvantages include loss by evaporationand/or migration from the propellant system wherein used. The propellantsystem may change considerably during long term storage as a result of aloss by evaporation and/or migration. The reliability of a propellantsystem may also change when such loss has occurred.

Since the vapor pressure of vinyl ferrocene would be lessened whenchanged to a form such as in a polymeric state, an approach topreventing loss by evaporation and/or migration would be to combinevinyl ferrocene with a polymeric binder. The problem of crystallizationof vinyl ferrocene in the propellant composition when stored at lowtemperature would be also eliminated if the vinyl ferrocene resided as apart of a copolymer in a polymeric chain.

An object of this invention is to provide copolymers of vinyl ferroceneand butadiene which have no significant vapor pressure and which do notcrystallize in the propellant when stored at relative low temperatures.

Another object is to provide vinyl ferrocene copolymers usable inpropellant compositions as a replacement for the liquid ferrocenecatalyst and as a replacement for part of the normally used binders.

A further object is to provide copolymers of vinyl ferrocene by aprocess whereby the iron content in the finished copolymers as well asthe molecular weight of the copolymers are controllable.

SUMMARY OF THE INVENTION Vinyl ferrocene and butadiene are copolymerizedin an inert organic solvent (e.g., benzene, toluene, and the like) underredox conditions by a suitable catalyst (e.g.,

ice

cyclohexanone peroxide) to provide, in 50 percent or better yield, acopolymer having a suitable iron content for use in propellants as areplacement for the burning rate catalyst thereof. The copolymers alsohave suitable molecular weights and binder properties for use as apartial replacement for the normally used binders of propellantcompositions. A representative copolymer of this invention has anaverage molecular weight of about 860 and an iron content of about 10.2percent. The representative copolymer is utilized in a compositepropellant composition having additional ingredients comprised ofcarboxyterminated polybutadiene binder, ammonium perchlorate oxidizer,and aluminum metal fuel. The propellant having about 1 weight percentiron content showed a burning rate superior to propellants having anequal amount of iron content While in a propellant as n-butyl ferroceneand Fe O Although a partial replacement of carboxyterminated binder wasmade by the vinyl ferrocene-butadiene copolymer, the physical propertiesof the propellant composition were maintained at a satisfactory level.The gain in benefit of having the catalyst widely distributed as part ofthe stable polymeric binder is a significant one since the propellantburning rate is higher at all pressures than the standards usingn-butylferrocene and F3203.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Copolymers of vinyl ferroceneand butadiene with controllable molecular weight and iron content areobtained in the following general manner. A three neck flask fitted witha stirrer, a cold finger, and dropping funnel is used. About 200milliliters (ml..) of distilled water is added to the flask and thesystem is degassed by boiling. Then 4.75 ml. of a non-ionic surfactant,wetting agent (e.g., Triton 102 supplied by Rohm and Haas Co. issatisfactory), 15 ml. of benzene, 6.75 grams of vinyl ferrocene, 27grams of butadiene, and 4.72 grams of ferrous sulfate are added at 0 C.Then cyclohexanone peroxide (5.75 grams of cyclohexanone peroxide in 40milliliters of tetrahydrofuran solution of 0 C.) is added in increments,while the reaction mixture at 0 C. is agitated, for a period of time ofabout one hour. The reaction mixture is then poured into 800 cc. of H 0,made acidic with HCl, and extracted 4 times with 300 ml. of benzene. Thebenzene layer is Water washed, dried over Na SO and aspirated. The crudepolymer is then obtained in 50 percent or better yield. Furtherpurification is accomplished by pumping at 2 mm. Hg and 130 C. in acommercial sublimator for three days to remove (by sublimation)remaining traces of vinyl ferrocene. The polymer is soluble in mostorganic solvents. The molecular weight in the run described above isabout 860 when measured on a vapor pressure osmometer. The percentage ofthe Fe in the polymer is 10.2%. The infrared spectrum contains bands fora relatively free carboxylic acid group (3400 cm.- and 1620 CHstretching both below and above 3000 cm.- indicating aliphatic andcyclopentadienyl rings are present, a band at 965 cm.- which. inaddition to absorption in the 1600 cm. region provides some support ofthe presence of trans double bands. A large band at 825 cm." is commonlyfound in ferrocene compounds. In common with other monosubstitutedferrocene compounds, bands are present at cm. and 1000 cmr 0n the basisof the percent Fe and the numerical average molecular weight of thepolymer, calculations indicate that about 6.2 butadiene molecules arepresent for every molecule of vinyl ferrocene in the average molecule.

The product specified above shows an intrinic viscosity indichloroethane of 0.0014. The polymer is fractionated by columnchromatography on alumina and the eluted fractions have infrared spectraidentical to the crude polymer. I

The ferrous sulfate provides a reducing material for the reactions whichproceed under redox conditions whereby the peroxide catalyst (e.g.,cyclohexanone peroxide) is reduced and serves to terminate the chain ofthe polymers formed. Although the exact structure of the vinyl ferrocenebutadiene copolymers are not known conclusively, the copolymers of thisinvention include cyclohexanone peroxide chain termination. The generalrepresentative structure for the cyclohexanone peroxide chain terminatedcopolymer of vinyl ferrocene and butadiene is illustrated as follows:

Burning rate studies have been made with the polymers of this inventionon propellants comprised of carboxyterminated polybutadiene (CTP-B)binder, powdered aluminum metal fuel, and ammonium perchlorate oxidizer.A typical propellant sample (No. 1) set forth below using vinylferrocene-butadiene copolymer is compared with a standard propellant(No. 2), using n-butyl ferrocene (NBF), and a propellant sample (No. 3),using Fe O as the catalyst.

P ROPELLANT SAMPLE S No. 1, No; 2, No. 3, wt. percent wt. percent wt.percent Total 100. 00 100. 00 100. 00

VFGTPB (polymer). 1 NB F. F830 3.

The burning rates of samples No. 1, No. 2, and No. 3, each containingthe equivalent weight of specified material to yield 1% Fe, are setforth below.

The process of this invention is carried out in a suitable containerwhich is subjected to a controlled environment for maintaining thepredetermined reaction temperature, for preventing loss of volatilecomponents, and for providing agitation to maintain uniformity andmixing of reactant with reaction mixture to produce polymers ofcontrolled molecular weights and iron contents. A predetermined reactiontemperature and time, concentration, and rate of peroxide addition willpermit many desirable combinations to yield the desired products. Onecan vary the reaction temperature, the rate of catalyst addition, theweight ratio of butadiene to vinyl ferrocene, and the total amount ofcyclohexanone peroxide or other suitable organic peroxide catalyst andreactant added to produce copolymers having wide molecular weight rangesand total percentages of iron. A higher reaction temperature yieldslower molecular weights at same catalyst addition rate. At sametemperature, a slower catalyst addition rate yields a higher molecularweight polymer. The molecular weight range of polymers obtained by theprocess conditions set 4 forth hereinabove is from about 400 to about2,000 with an average of about 860.

When a ratio of butadiene (4) to vinyl ferrocene (l) is used, a polymerof about 10.2 weight percent iron is obtained. Thus, a dilution of thedescribed polymer of about 10 to 1 in the propellant mix, provides about1% Fe content. A ratio of about 6 parts butadiene to about 1 part vinylferrocene would yield a polymer of less iron content, assuming otherconditions were maintained. It follows that the quantity of thiscopolymer could be increased when used in the propellant samples asabove to provide the desired iron content in the finished propellant,and a higher percent of the binder could be replaced with the copolymerspecified.

Other inert organic solvents with properties similar to benzene areusable with the process of this invention. Other lower oxidation statesof metallic salts such as bivalent metallic salts of nickel or cobaltcan be used in place of ferrous sulfate. Other organic peroxides such ascumene hydroperoxide or tert-butyl hydroperoxide can be employed as thecatalyst and chain terminator in the process of this invention. Theorganic peroxides in a compatible solvent (e.g., tetrahydrofuran) arepreferably added over a predetermined period of time to obtain thedesired product having controlled iron content and molecular weight.

The wetting agent should be a non-ionic surfactant based on alkylarylpolyether alcohols whose surface activity includes wetting andemulsification and is suitable for use in polymer manufacture.

The suitable container adapted for receiving the reactants, should alsobe adapted with a cooling means to maintain the predetermined reactiontemperature selected for obtaining desired molecular weight. Thecontainer should be equipped with a means suitable for preventing lossof volatile components such as butadiene from the reaction containerduring the reaction phase. A cold finger, (e.g., a cold column), such asone packed with Dry Ice whose function would be similar to a refluxapparatus whereby volatile components are condensed and returned to thereaction mitxure, works very well for the described function. Thecontainer should be equipped with agitation means during reaction todistribute the reactant within reaction mixture and maintain uniformityof concentrations, temperatures, etc.

The vinyl ferrocene-butadiene copolymers of this invention may be usedin the propellant composition in an amount from about 5 weight percentto about 25 weight percent. The remaining propellant ingredientsexclusive of processing aids (such as lecithin and trace amount ofadditives) may be comprised of carboxyterminated polybutadiene binder,plasticizer, a metal fuel such as aluminum, and an inorganic oxidizersuch as ammonium perchlorate.

Since the burning rate of a propellant increases as the iron contentincreases, optimum amounts of iron content can be controlled at leasttwo ways. The amount of vinyl ferrocene copolymerized with butadiene aswell as the amount of copolymer selected for use in formulations are twoways whereby the desired iron content, burning rate, and physicalproperties may be optimized.

Those skilled in the art will recognize that other propellantingredients may be varied to include metal additives other than aluminumin amount from about 5 to about 20 weight percent, inorganic oxidizersuch as ammonium perchlorate from about 10 to about 72 weight percent.Plasticizers (e.g., non-volatile organic liquids or low melting pointsolids such as phthalic, adipate, and sebacate esters and aryl phosphateesters) may be selected for use with the copolymers of this invention.Plasticizer content is determined by the desirable properties requiredfor a propellant formulation. Generally, plasticizer amount from about 5to about 30 weight percent is satisfactory. Since the copolymers of thisinvention are easily blended with the remaining binder and otheringredients no additional plasticizer is required in most instances.Special curing agents and trace amount of additives known in the art fortheir specific contribution to the ballistic, castibility, and storageproperties of the propellant may be added to the propellant formulationwithout interfering with the functions of the vinyl ferrocene-butadienecopolymers.

We claim:

1. The carboxyterminated-copolymers of vinyl ferrocene and butadienecharacterized by having a controlled iron content and molecular weight,said copolymers being formed in a reaction mixture by the process whichcomprises combining a predetermined weight ratio of vinyl ferrocene andbutadiene, a lower oxidation state metallic salt selected from thebivalent metallic salts of iron, nickel, and cobalt, a suitablenon-ionic surfactant, and an inert organic solvent selected from benzeneand toluene; containing said reaction mixture in a suitable containerthat is subjected to a controlled environment for maintaining apredetermined temperature of said reaction mixture during the reactionphase when said copolymers are formed and for preventing loss ofvolatile components from said reaction mixture; agitating said reactionmixture during said reaction phase; adding in increments to saidreaction mixture over a predetermined period of time a. reactantselected from cyclohexanone peroxide, cumene hydroperoxide, andtert-butyl hydroperoxide, and which is contained in a compatiblesolvent, to thereby form said copolymers; and thereafter separating saidcopolymers.

2. The copolymers prepared in accordance with the process of claim 1 andwherein said suitable non-ionic surfactant is present in an amount ofabout 4.75 milliliters, said inert organic solvent is benzene in anamount of about 15 milliliters, said predetermined weight ratio is about6.75

grams of vinyl ferrocene to about 27 grams of butadiene, said loweroxidation state metallic salt is ferrous sulfate in an amount of about4.72 grams; said reactant is cyclohexanone peroxide in the amount ofabout 5.75 grams contained in about milliliters of the compatiblesolvent, said compatible solvent being te'trahydrofuran, and saidpredetermined period of time for adding said reactant to said reactionmixture is about one hour while a predetermined temperature of reactionmixture and reactant is maintained at about 0 C.

3. The copolymers of claim 2 and wherein said copolymers arecharacterized by having a controlled iron content of about 10.2 weightpercent and by having a controlled molecular weight range from about 400to about 2000 with an average molecular weight of about 860.

Arimoto et al.: J. Am. Chem. Soc., 77, 6295-7. Baldwin et al.: J.Polymer Science, Part Al, 5, 2091-8. Pittman: J. Polymer Science, PartB, 6, 19-21.

CARL D. QUARFORTH, Primary Examiner E. A. MILLER, Assistant Examiner US.Cl. XR. 26082.l

